Even if you have the best valvetrain components in your race engine, improper installation and alignment can leave it huffing and wheezing like a back-of-the-pack hunk of junk. Worse, poor valvetrain alignment will lead to accelerated wear which can cause parts to wear out and break before you even make it to rebuild time.
1 Most cylinder heads for...
1 Most cylinder heads for Chevrolet small-blocks have bolt holes for the rocker studs that are open to the water jacket. If you don't apply thread seal to the rocker studs, this is a guaranteed coolant leak.
There are also plenty of times you may need to work on your race engine's valvetrain for general maintenance. Inexpensive stock valvesprings in crate engines help manage costs, but they are also prone to losing pressure and must be replaced regularly. Engines running flat tappet lifters must also have the lash on all the valves regularly checked. Finally, you may attempt to repair or rebuild your own race engine and must make sure that the valvetrain is assembled as well as possible.
While reassembling Circle Track's Dyno Mule Chevy 350 for an upcoming story, we also had the opportunity to try out Lunati's new Voodoo aluminum rocker arms. These new Lunati rockers are full roller to minimize friction and feature oiling galleries to lubricate and cool the valvesprings as well as the trunion and roller tip. They are also machined to provide plenty of clearance for high-lift aggressive cam profiles--which fits the need for the solid roller Comp camshaft we're using that produces 0.610 lift at the valve.
We'll fire up the dyno mule in a future issue for some interesting tests. But in the meantime, we thought we'd pass along a few tips for making sure your valvetrain is working as efficiently as possible. So without further ado, here they are.
2 The rocker studs don't...
2 The rocker studs don't require Loctite but should all be torqued to 50 ft-lb using thread seal as the only lubricant.
3 We were lucky to get our...
3 We were lucky to get our hands on Lunati's new aluminum Voodoo rocker arms. These are 1.5:1 ratio, feature full roller trunions and roller tips, and should be quite competitive price-wise to other performance rockers on the market.
4 The rockers have oiling...
4 The rockers have oiling galleries to feed oil to both the roller tip and the valvespring to help keep it cool. Also notice that the underside of the rocker has been machined to create room for large diameter racing springs and high-lift camshaft profiles.
5 After submerging the Comp...
5 After submerging the Comp Cams solid roller lifters in motor oil, they were installed in the lifter bores.
6 Since this is the first...
6 Since this is the first time we've run this engine combo with the new Lunati rockers, we had to make sure the pushrods are the correct length. This is an easy process and should be done any time you make a change in the valvetrain components you are using.
7 If this is a new build...
7 If this is a new build or you don't have a variety of different pushrod lengths on hand for testing, you can use a pushrod length checker like this one from Powerhouse Products. The checker is essentially a short pushrod that uses a piece of threaded rod so it can be extended. Because of the threaded rod, the checking pushrod isn't very strong, so if you use one it's definitely recommended to swap out the standard valvespring for a lightweight check spring such as the one you see here. If you don't, it's likely you'll wind up with a bent checking pushrod and a lot of frustration.
8 The length of the pushrod...
8 The length of the pushrod determines where the tip of the rocker arm contacts the top of the valve stem. To check for proper pushrod length, begin by
9 Next, install the rocker...
9 Next, install the rocker arm and install the lock nut so that you have zero lash.
10 Bump the engine over several...
10 Bump the engine over several revolutions so that the valve you are checking opens and closes a few times. With roller rockers, it helps to hold your thumb over the roller tip so that it doesn't roll quite so easily. This helps make the mark it leaves on the tip of the valve stem more defined.
11 Here, you can see the...
11 Here, you can see the difference in two different pushrod lengths. We started with the intake valve with an 8.000-inch pushrod from Comp Cams (right). It's just a bit too short, which you can tell because the mark it left on the tip of the valve stem is slightly above center. If the pushrod is too long, the mark will be below the centerline of the valve stem tip. We tried again with the exhaust valve (left) using an 8.100-inch pushrod that turned out to be perfect.
12 Here's a shot of the two...
12 Here's a shot of the two Comp pushrods we used. As you can see, there isn't much difference in length between the too-short 8.000-inch pushrod and the just-right 8.100-inch unit, but it makes a big difference in how the rocker arm contacts the valve stem. If the rocker tip isn't centered over the valve stem, it can push the stem against the guide and cause excessive wear and--eventually--a dropped valve.
13 Once you have your correct...
13 Once you have your correct pushrods, take a moment to clean them thoroughly. Even if they are brand-new, make sure that the hollow centers are clean and free of debris. This is how your engine oils the rocker, so if one is clogged it can mean big problems. If you don't have a pushrod brush like this, at least blow compressed air through each one of the hollow centers.
14 Before installing your...
14 Before installing your rocker arms for the final time, check to make sure the trunion pivots are oriented properly. A flat is machined on one side (right in this photo) to provide a solid pressure face for the locking nut. Make sure the flat is pointing up on every rocker.
15 Check with your camshaft...
15 Check with your camshaft manufacturer for the suggested valve lash if you're running a solid cam. Normally, lash for a race motor is around 0.018-inch on the intake valves and 0.020 on the exhausts. You can check this with a feeler gauge. Use the lock nut to add or remove lash. If you're running a hydraulic cam, the usual practice is to tighten the lock nut until all the lash is removed (spin the pushrod while tightening the nut until you begin to feel some drag on the pushrod), and then tighten it an additional half-turn. If this is final assembly, a little extreme pressure lube between the end of the pushrod and the lifter's pushrod cup will help protect this area during initial start up.
16 Once you have the proper...
16 Once you have the proper lash, tighten the locking screw inside the nut to lock it down. Once you have everything set, double check to make sure your lash didn't change while tightening everything down.
17 Lash should only be checked...
17 Lash should only be checked when the lifter for the valve you are checking is on the camshaft's base circle, which means the valve is fully closed and you have full lash available. The easiest way to do this is to use the
18 Here's the rocker fully...
18 Here's the rocker fully lashed and ready to go. Notice that the roller tip contacts the tip of the valvestem just above the center.
19 As the valve opens, the...
19 As the valve opens, the tip of the rocker rolls across the center of the valve stem tip and slightly to the bottom side. And as the valve closes it takes the same route in reverse. This limits side forces on your valves to help them live long, happy lives and also provides the correct geometry so that those valves are opening and closing exactly when your precisely ground camshaft says they should.